Packet metering was introduced in IEEE 802.1ad-2005 with a Drop Eligible Indicator (DEI) and in IEEE 802.1Q-2011 with a Canonical Format Indicator (CFI) to allow for packet “color” (drop eligibility). A packet's color is different from its priority. Priority is an inherent characteristic of a packet, determined by the contents. Different priorities can be mapped to different traffic classes, queued in different queues, and do not need order to be maintained between packets of different priorities. Color, on the other hand, is not an inherent characteristic of a packet and is determined based on the arrival time at a meter relative to the history of arrival times of previous packets. Frames within a traffic class can be marked different colors. An exemplary three color system utilizes Green, Yellow, and Red. Green can be for committed packets, Yellow for excess packets, and Red for non-conformant (discard) packets which are discarded. One example metering algorithm is described in Internet Engineering Task Force (IETF) Request for Comments (RFC) 4115 (July 2005), “A Differentiated Service Two-Rate, Three-Color Marker with Efficient Handling of in-Profile Traffic,” the contents of which are incorporated by reference. Note, the term packet can also reference a frame as described herein.
RFC 4115 defines the behavior of a meter in terms of its mode and two token buckets, C and E (Committed and Excess, respectively, note C=Green and E=Yellow), with the rates, CIR (Committed Information Rate) and EIR (Excess Information Rate), respectively, and maximum sizes CBS (Committed Burst Size) and EBS (Excess Burst Size). The token buckets C and E are initially (at time 0) full; i.e., the token count Tc(0)=CBS and Te(0)=EBS. Thereafter, the token count Tc is incremented by one CIR times per second (up to CBS), and the token count Te is incremented by one EIR times per second (up to EBS). For a “Differentiated Service Two-Rate, Three-Color Marker” complying RFC 4115, there can be a situation where traffic is busty in nature but under the metering limit (EIR) such that all traffic ingressing/coming is Ethernet Virtual Local Area Network (VLAN) Tagged with CFI set thus using EBS bucket only. Due to the bursty nature of traffic, this situation of long bursts can lead to dropped packets even though traffic is within metering limits. This drop of packets happens due to the unavailability of tokens because overflowed tokens from EBS were wasted.